I believe I saw P705BTA yesterday, in all-white livery, heading north of Loughton towards the M11/M25. Maybe on it's way to Roadrunner?

(1000 posts! )

It could of been on Lea Valley Buses route 255 or 555, as these routes pass the Waltham Abbey M25 junction. Lea Valley has a connection with Roadrunner, as the MD of Lea Valley used to be/still is MD for Roadrunner. Not sure if there is a definate link though.